Quote Originally Posted by johnboy View Post
It's hard to say definitively; but I'm pretty sure you've nailed it Roger.
It appears that the strata is horizontal and the drill holes upandicular, i.e. angled back from the roadway; but straight up and down within that plane.

I'm picking it was done (as you intimated,) so that the excavator operator could shear the face off more accurately; like tearing stamps off a serrated sheet.

It's just I've never seen that done before.
It's seen a lot in the US, where they attempt to reduce sharp grade changes on major highways to improve trucking efficiency and allow more consistent speed without overly affecting efficiency. A civil/structural buddy that I worked with for years offered:
My personal thought whenever I see those bore holes is that is what is left behind after the blast. I’ve always assumed the holes were drilled near a free edge and the majority of the force of the blast chose the path of least resistance, leaving a half circle behind. I’ll see if anyone around here has a better answer.
I haven't heard anything more from him.